Length Dependence of Tunneling Current Through Single Phenylene Oligomers Measured by Scanning Tunneling Microscopy at Low Temperature

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The length dependence of tunneling current through single phenylene oligomers, i.e., benzenemethanethiol, 4-biphenylmethanethiol and [1,1$'$:4$'$,1$''$-terphenyl]-4-methanethiol, was determined experimentally by scanning tunneling microscopy (STM). The single phenylene oligomers were isolated in a self-assembled monolayer (SAM) matrix of a disulfide with two spherical bicyclo[2.2.2]octane moieties on Au(111). The STM measurement was conducted at a low temperature to prevent the thermal motions of the isolated molecules that occur at room temperature. The isolated single molecules inserted in the SAM matrix were observed as protrusions in an STM topography using a constant-current mode owing to their higher tunneling ability. The decay constant, $\beta$, of the tunneling current through single phenylene oligomers was estimated from the STM heights of the protrusions corresponding to the single phenylene oligomers using a bilayer tunnel junction model. The value of $\beta$ for tunneling current through single phenylene oligomers was $5.5 \pm 0.2$ nm-1. In a constant-height mode, we measured the conductance of the isolated single molecules. We estimated an averaged single-molecular conductance of the isolated molecules of a biphenyl derivative to be ca. 2 nS. Here, one side of each isolated molecule was bound via an Au–S bond and the other phenyl end was physically in contact with an Au STM tip.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2006-04-15

Length Dependence of Tunneling Current Through Single Phenylene Oligomers Measured by Scanning Tunneling Microscopy at Low Temperature

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